diff options
Diffstat (limited to 'kex.c')
| -rw-r--r-- | kex.c | 1378 |
1 files changed, 1378 insertions, 0 deletions
@@ -0,0 +1,1378 @@ +/* $OpenBSD: kex.c,v 1.159 2020/07/05 23:59:45 djm Exp $ */ +/* + * Copyright (c) 2000, 2001 Markus Friedl. All rights reserved. + * + * Redistribution and use in source and binary forms, with or without + * modification, are permitted provided that the following conditions + * are met: + * 1. Redistributions of source code must retain the above copyright + * notice, this list of conditions and the following disclaimer. + * 2. Redistributions in binary form must reproduce the above copyright + * notice, this list of conditions and the following disclaimer in the + * documentation and/or other materials provided with the distribution. + * + * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR + * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES + * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. + * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, + * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT + * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, + * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY + * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT + * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF + * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. + */ + +#include "includes.h" + +#include <sys/types.h> +#include <errno.h> +#include <signal.h> +#include <stdarg.h> +#include <stdio.h> +#include <stdlib.h> +#include <string.h> +#include <unistd.h> +#ifdef HAVE_POLL_H +#include <poll.h> +#endif + +#ifdef WITH_OPENSSL +#include <openssl/crypto.h> +#include <openssl/dh.h> +#endif + +#include "ssh.h" +#include "ssh2.h" +#include "atomicio.h" +#include "version.h" +#include "packet.h" +#include "compat.h" +#include "cipher.h" +#include "sshkey.h" +#include "kex.h" +#include "log.h" +#include "mac.h" +#include "match.h" +#include "misc.h" +#include "dispatch.h" +#include "monitor.h" + +#include "ssherr.h" +#include "sshbuf.h" +#include "digest.h" + +/* prototype */ +static int kex_choose_conf(struct ssh *); +static int kex_input_newkeys(int, u_int32_t, struct ssh *); + +static const char *proposal_names[PROPOSAL_MAX] = { + "KEX algorithms", + "host key algorithms", + "ciphers ctos", + "ciphers stoc", + "MACs ctos", + "MACs stoc", + "compression ctos", + "compression stoc", + "languages ctos", + "languages stoc", +}; + +struct kexalg { + char *name; + u_int type; + int ec_nid; + int hash_alg; +}; +static const struct kexalg kexalgs[] = { +#ifdef WITH_OPENSSL + { KEX_DH1, KEX_DH_GRP1_SHA1, 0, SSH_DIGEST_SHA1 }, + { KEX_DH14_SHA1, KEX_DH_GRP14_SHA1, 0, SSH_DIGEST_SHA1 }, + { KEX_DH14_SHA256, KEX_DH_GRP14_SHA256, 0, SSH_DIGEST_SHA256 }, + { KEX_DH16_SHA512, KEX_DH_GRP16_SHA512, 0, SSH_DIGEST_SHA512 }, + { KEX_DH18_SHA512, KEX_DH_GRP18_SHA512, 0, SSH_DIGEST_SHA512 }, + { KEX_DHGEX_SHA1, KEX_DH_GEX_SHA1, 0, SSH_DIGEST_SHA1 }, +#ifdef HAVE_EVP_SHA256 + { KEX_DHGEX_SHA256, KEX_DH_GEX_SHA256, 0, SSH_DIGEST_SHA256 }, +#endif /* HAVE_EVP_SHA256 */ +#ifdef OPENSSL_HAS_ECC + { KEX_ECDH_SHA2_NISTP256, KEX_ECDH_SHA2, + NID_X9_62_prime256v1, SSH_DIGEST_SHA256 }, + { KEX_ECDH_SHA2_NISTP384, KEX_ECDH_SHA2, NID_secp384r1, + SSH_DIGEST_SHA384 }, +# ifdef OPENSSL_HAS_NISTP521 + { KEX_ECDH_SHA2_NISTP521, KEX_ECDH_SHA2, NID_secp521r1, + SSH_DIGEST_SHA512 }, +# endif /* OPENSSL_HAS_NISTP521 */ +#endif /* OPENSSL_HAS_ECC */ +#endif /* WITH_OPENSSL */ +#if defined(HAVE_EVP_SHA256) || !defined(WITH_OPENSSL) + { KEX_CURVE25519_SHA256, KEX_C25519_SHA256, 0, SSH_DIGEST_SHA256 }, + { KEX_CURVE25519_SHA256_OLD, KEX_C25519_SHA256, 0, SSH_DIGEST_SHA256 }, + { KEX_SNTRUP4591761X25519_SHA512, KEX_KEM_SNTRUP4591761X25519_SHA512, 0, + SSH_DIGEST_SHA512 }, +#endif /* HAVE_EVP_SHA256 || !WITH_OPENSSL */ + { NULL, 0, -1, -1}, +}; + +char * +kex_alg_list(char sep) +{ + char *ret = NULL, *tmp; + size_t nlen, rlen = 0; + const struct kexalg *k; + + for (k = kexalgs; k->name != NULL; k++) { + if (ret != NULL) + ret[rlen++] = sep; + nlen = strlen(k->name); + if ((tmp = realloc(ret, rlen + nlen + 2)) == NULL) { + free(ret); + return NULL; + } + ret = tmp; + memcpy(ret + rlen, k->name, nlen + 1); + rlen += nlen; + } + return ret; +} + +static const struct kexalg * +kex_alg_by_name(const char *name) +{ + const struct kexalg *k; + + for (k = kexalgs; k->name != NULL; k++) { + if (strcmp(k->name, name) == 0) + return k; + } + return NULL; +} + +/* Validate KEX method name list */ +int +kex_names_valid(const char *names) +{ + char *s, *cp, *p; + + if (names == NULL || strcmp(names, "") == 0) + return 0; + if ((s = cp = strdup(names)) == NULL) + return 0; + for ((p = strsep(&cp, ",")); p && *p != '\0'; + (p = strsep(&cp, ","))) { + if (kex_alg_by_name(p) == NULL) { + error("Unsupported KEX algorithm \"%.100s\"", p); + free(s); + return 0; + } + } + debug3("kex names ok: [%s]", names); + free(s); + return 1; +} + +/* + * Concatenate algorithm names, avoiding duplicates in the process. + * Caller must free returned string. + */ +char * +kex_names_cat(const char *a, const char *b) +{ + char *ret = NULL, *tmp = NULL, *cp, *p, *m; + size_t len; + + if (a == NULL || *a == '\0') + return strdup(b); + if (b == NULL || *b == '\0') + return strdup(a); + if (strlen(b) > 1024*1024) + return NULL; + len = strlen(a) + strlen(b) + 2; + if ((tmp = cp = strdup(b)) == NULL || + (ret = calloc(1, len)) == NULL) { + free(tmp); + return NULL; + } + strlcpy(ret, a, len); + for ((p = strsep(&cp, ",")); p && *p != '\0'; (p = strsep(&cp, ","))) { + if ((m = match_list(ret, p, NULL)) != NULL) { + free(m); + continue; /* Algorithm already present */ + } + if (strlcat(ret, ",", len) >= len || + strlcat(ret, p, len) >= len) { + free(tmp); + free(ret); + return NULL; /* Shouldn't happen */ + } + } + free(tmp); + return ret; +} + +/* + * Assemble a list of algorithms from a default list and a string from a + * configuration file. The user-provided string may begin with '+' to + * indicate that it should be appended to the default, '-' that the + * specified names should be removed, or '^' that they should be placed + * at the head. + */ +int +kex_assemble_names(char **listp, const char *def, const char *all) +{ + char *cp, *tmp, *patterns; + char *list = NULL, *ret = NULL, *matching = NULL, *opatterns = NULL; + int r = SSH_ERR_INTERNAL_ERROR; + + if (listp == NULL || def == NULL || all == NULL) + return SSH_ERR_INVALID_ARGUMENT; + + if (*listp == NULL || **listp == '\0') { + if ((*listp = strdup(def)) == NULL) + return SSH_ERR_ALLOC_FAIL; + return 0; + } + + list = *listp; + *listp = NULL; + if (*list == '+') { + /* Append names to default list */ + if ((tmp = kex_names_cat(def, list + 1)) == NULL) { + r = SSH_ERR_ALLOC_FAIL; + goto fail; + } + free(list); + list = tmp; + } else if (*list == '-') { + /* Remove names from default list */ + if ((*listp = match_filter_denylist(def, list + 1)) == NULL) { + r = SSH_ERR_ALLOC_FAIL; + goto fail; + } + free(list); + /* filtering has already been done */ + return 0; + } else if (*list == '^') { + /* Place names at head of default list */ + if ((tmp = kex_names_cat(list + 1, def)) == NULL) { + r = SSH_ERR_ALLOC_FAIL; + goto fail; + } + free(list); + list = tmp; + } else { + /* Explicit list, overrides default - just use "list" as is */ + } + + /* + * The supplied names may be a pattern-list. For the -list case, + * the patterns are applied above. For the +list and explicit list + * cases we need to do it now. + */ + ret = NULL; + if ((patterns = opatterns = strdup(list)) == NULL) { + r = SSH_ERR_ALLOC_FAIL; + goto fail; + } + /* Apply positive (i.e. non-negated) patterns from the list */ + while ((cp = strsep(&patterns, ",")) != NULL) { + if (*cp == '!') { + /* negated matches are not supported here */ + r = SSH_ERR_INVALID_ARGUMENT; + goto fail; + } + free(matching); + if ((matching = match_filter_allowlist(all, cp)) == NULL) { + r = SSH_ERR_ALLOC_FAIL; + goto fail; + } + if ((tmp = kex_names_cat(ret, matching)) == NULL) { + r = SSH_ERR_ALLOC_FAIL; + goto fail; + } + free(ret); + ret = tmp; + } + if (ret == NULL || *ret == '\0') { + /* An empty name-list is an error */ + /* XXX better error code? */ + r = SSH_ERR_INVALID_ARGUMENT; + goto fail; + } + + /* success */ + *listp = ret; + ret = NULL; + r = 0; + + fail: + free(matching); + free(opatterns); + free(list); + free(ret); + return r; +} + +/* put algorithm proposal into buffer */ +int +kex_prop2buf(struct sshbuf *b, char *proposal[PROPOSAL_MAX]) +{ + u_int i; + int r; + + sshbuf_reset(b); + + /* + * add a dummy cookie, the cookie will be overwritten by + * kex_send_kexinit(), each time a kexinit is set + */ + for (i = 0; i < KEX_COOKIE_LEN; i++) { + if ((r = sshbuf_put_u8(b, 0)) != 0) + return r; + } + for (i = 0; i < PROPOSAL_MAX; i++) { + if ((r = sshbuf_put_cstring(b, proposal[i])) != 0) + return r; + } + if ((r = sshbuf_put_u8(b, 0)) != 0 || /* first_kex_packet_follows */ + (r = sshbuf_put_u32(b, 0)) != 0) /* uint32 reserved */ + return r; + return 0; +} + +/* parse buffer and return algorithm proposal */ +int +kex_buf2prop(struct sshbuf *raw, int *first_kex_follows, char ***propp) +{ + struct sshbuf *b = NULL; + u_char v; + u_int i; + char **proposal = NULL; + int r; + + *propp = NULL; + if ((proposal = calloc(PROPOSAL_MAX, sizeof(char *))) == NULL) + return SSH_ERR_ALLOC_FAIL; + if ((b = sshbuf_fromb(raw)) == NULL) { + r = SSH_ERR_ALLOC_FAIL; + goto out; + } + if ((r = sshbuf_consume(b, KEX_COOKIE_LEN)) != 0) { /* skip cookie */ + error("%s: consume cookie: %s", __func__, ssh_err(r)); + goto out; + } + /* extract kex init proposal strings */ + for (i = 0; i < PROPOSAL_MAX; i++) { + if ((r = sshbuf_get_cstring(b, &(proposal[i]), NULL)) != 0) { + error("%s: parse proposal %u: %s", __func__, + i, ssh_err(r)); + goto out; + } + debug2("%s: %s", proposal_names[i], proposal[i]); + } + /* first kex follows / reserved */ + if ((r = sshbuf_get_u8(b, &v)) != 0 || /* first_kex_follows */ + (r = sshbuf_get_u32(b, &i)) != 0) { /* reserved */ + error("%s: parse: %s", __func__, ssh_err(r)); + goto out; + } + if (first_kex_follows != NULL) + *first_kex_follows = v; + debug2("first_kex_follows %d ", v); + debug2("reserved %u ", i); + r = 0; + *propp = proposal; + out: + if (r != 0 && proposal != NULL) + kex_prop_free(proposal); + sshbuf_free(b); + return r; +} + +void +kex_prop_free(char **proposal) +{ + u_int i; + + if (proposal == NULL) + return; + for (i = 0; i < PROPOSAL_MAX; i++) + free(proposal[i]); + free(proposal); +} + +/* ARGSUSED */ +static int +kex_protocol_error(int type, u_int32_t seq, struct ssh *ssh) +{ + int r; + + error("kex protocol error: type %d seq %u", type, seq); + if ((r = sshpkt_start(ssh, SSH2_MSG_UNIMPLEMENTED)) != 0 || + (r = sshpkt_put_u32(ssh, seq)) != 0 || + (r = sshpkt_send(ssh)) != 0) + return r; + return 0; +} + +static void +kex_reset_dispatch(struct ssh *ssh) +{ + ssh_dispatch_range(ssh, SSH2_MSG_TRANSPORT_MIN, + SSH2_MSG_TRANSPORT_MAX, &kex_protocol_error); +} + +static int +kex_send_ext_info(struct ssh *ssh) +{ + int r; + char *algs; + + debug("Sending SSH2_MSG_EXT_INFO"); + if ((algs = sshkey_alg_list(0, 1, 1, ',')) == NULL) + return SSH_ERR_ALLOC_FAIL; + /* XXX filter algs list by allowed pubkey/hostbased types */ + if ((r = sshpkt_start(ssh, SSH2_MSG_EXT_INFO)) != 0 || + (r = sshpkt_put_u32(ssh, 1)) != 0 || + (r = sshpkt_put_cstring(ssh, "server-sig-algs")) != 0 || + (r = sshpkt_put_cstring(ssh, algs)) != 0 || + (r = sshpkt_send(ssh)) != 0) { + error("%s: compose: %s", __func__, ssh_err(r)); + goto out; + } + /* success */ + r = 0; + out: + free(algs); + return r; +} + +int +kex_send_newkeys(struct ssh *ssh) +{ + int r; + + kex_reset_dispatch(ssh); + if ((r = sshpkt_start(ssh, SSH2_MSG_NEWKEYS)) != 0 || + (r = sshpkt_send(ssh)) != 0) + return r; + debug("SSH2_MSG_NEWKEYS sent"); + ssh_dispatch_set(ssh, SSH2_MSG_NEWKEYS, &kex_input_newkeys); + if (ssh->kex->ext_info_c && (ssh->kex->flags & KEX_INITIAL) != 0) + if ((r = kex_send_ext_info(ssh)) != 0) + return r; + debug("expecting SSH2_MSG_NEWKEYS"); + return 0; +} + +int +kex_input_ext_info(int type, u_int32_t seq, struct ssh *ssh) +{ + struct kex *kex = ssh->kex; + u_int32_t i, ninfo; + char *name; + u_char *val; + size_t vlen; + int r; + + debug("SSH2_MSG_EXT_INFO received"); + ssh_dispatch_set(ssh, SSH2_MSG_EXT_INFO, &kex_protocol_error); + if ((r = sshpkt_get_u32(ssh, &ninfo)) != 0) + return r; + for (i = 0; i < ninfo; i++) { + if ((r = sshpkt_get_cstring(ssh, &name, NULL)) != 0) + return r; + if ((r = sshpkt_get_string(ssh, &val, &vlen)) != 0) { + free(name); + return r; + } + if (strcmp(name, "server-sig-algs") == 0) { + /* Ensure no \0 lurking in value */ + if (memchr(val, '\0', vlen) != NULL) { + error("%s: nul byte in %s", __func__, name); + return SSH_ERR_INVALID_FORMAT; + } + debug("%s: %s=<%s>", __func__, name, val); + kex->server_sig_algs = val; + val = NULL; + } else + debug("%s: %s (unrecognised)", __func__, name); + free(name); + free(val); + } + return sshpkt_get_end(ssh); +} + +static int +kex_input_newkeys(int type, u_int32_t seq, struct ssh *ssh) +{ + struct kex *kex = ssh->kex; + int r; + + debug("SSH2_MSG_NEWKEYS received"); + ssh_dispatch_set(ssh, SSH2_MSG_NEWKEYS, &kex_protocol_error); + ssh_dispatch_set(ssh, SSH2_MSG_KEXINIT, &kex_input_kexinit); + if ((r = sshpkt_get_end(ssh)) != 0) + return r; + if ((r = ssh_set_newkeys(ssh, MODE_IN)) != 0) + return r; + kex->done = 1; + kex->flags &= ~KEX_INITIAL; + sshbuf_reset(kex->peer); + /* sshbuf_reset(kex->my); */ + kex->flags &= ~KEX_INIT_SENT; + free(kex->name); + kex->name = NULL; + return 0; +} + +int +kex_send_kexinit(struct ssh *ssh) +{ + u_char *cookie; + struct kex *kex = ssh->kex; + int r; + + if (kex == NULL) { + error("%s: no hex", __func__); + return SSH_ERR_INTERNAL_ERROR; + } + if (kex->flags & KEX_INIT_SENT) + return 0; + kex->done = 0; + + /* generate a random cookie */ + if (sshbuf_len(kex->my) < KEX_COOKIE_LEN) { + error("%s: bad kex length: %zu < %d", __func__, + sshbuf_len(kex->my), KEX_COOKIE_LEN); + return SSH_ERR_INVALID_FORMAT; + } + if ((cookie = sshbuf_mutable_ptr(kex->my)) == NULL) { + error("%s: buffer error", __func__); + return SSH_ERR_INTERNAL_ERROR; + } + arc4random_buf(cookie, KEX_COOKIE_LEN); + + if ((r = sshpkt_start(ssh, SSH2_MSG_KEXINIT)) != 0 || + (r = sshpkt_putb(ssh, kex->my)) != 0 || + (r = sshpkt_send(ssh)) != 0) { + error("%s: compose reply: %s", __func__, ssh_err(r)); + return r; + } + debug("SSH2_MSG_KEXINIT sent"); + kex->flags |= KEX_INIT_SENT; + return 0; +} + +/* ARGSUSED */ +int +kex_input_kexinit(int type, u_int32_t seq, struct ssh *ssh) +{ + struct kex *kex = ssh->kex; + const u_char *ptr; + u_int i; + size_t dlen; + int r; + + debug("SSH2_MSG_KEXINIT received"); + if (kex == NULL) { + error("%s: no hex", __func__); + return SSH_ERR_INTERNAL_ERROR; + } + ssh_dispatch_set(ssh, SSH2_MSG_KEXINIT, NULL); + ptr = sshpkt_ptr(ssh, &dlen); + if ((r = sshbuf_put(kex->peer, ptr, dlen)) != 0) + return r; + + /* discard packet */ + for (i = 0; i < KEX_COOKIE_LEN; i++) { + if ((r = sshpkt_get_u8(ssh, NULL)) != 0) { + error("%s: discard cookie: %s", __func__, ssh_err(r)); + return r; + } + } + for (i = 0; i < PROPOSAL_MAX; i++) { + if ((r = sshpkt_get_string(ssh, NULL, NULL)) != 0) { + error("%s: discard proposal: %s", __func__, ssh_err(r)); + return r; + } + } + /* + * XXX RFC4253 sec 7: "each side MAY guess" - currently no supported + * KEX method has the server move first, but a server might be using + * a custom method or one that we otherwise don't support. We should + * be prepared to remember first_kex_follows here so we can eat a + * packet later. + * XXX2 - RFC4253 is kind of ambiguous on what first_kex_follows means + * for cases where the server *doesn't* go first. I guess we should + * ignore it when it is set for these cases, which is what we do now. + */ + if ((r = sshpkt_get_u8(ssh, NULL)) != 0 || /* first_kex_follows */ + (r = sshpkt_get_u32(ssh, NULL)) != 0 || /* reserved */ + (r = sshpkt_get_end(ssh)) != 0) + return r; + + if (!(kex->flags & KEX_INIT_SENT)) + if ((r = kex_send_kexinit(ssh)) != 0) + return r; + if ((r = kex_choose_conf(ssh)) != 0) + return r; + + if (kex->kex_type < KEX_MAX && kex->kex[kex->kex_type] != NULL) + return (kex->kex[kex->kex_type])(ssh); + + error("%s: unknown kex type %u", __func__, kex->kex_type); + return SSH_ERR_INTERNAL_ERROR; +} + +struct kex * +kex_new(void) +{ + struct kex *kex; + + if ((kex = calloc(1, sizeof(*kex))) == NULL || + (kex->peer = sshbuf_new()) == NULL || + (kex->my = sshbuf_new()) == NULL || + (kex->client_version = sshbuf_new()) == NULL || + (kex->server_version = sshbuf_new()) == NULL) { + kex_free(kex); + return NULL; + } + return kex; +} + +void +kex_free_newkeys(struct newkeys *newkeys) +{ + if (newkeys == NULL) + return; + if (newkeys->enc.key) { + explicit_bzero(newkeys->enc.key, newkeys->enc.key_len); + free(newkeys->enc.key); + newkeys->enc.key = NULL; + } + if (newkeys->enc.iv) { + explicit_bzero(newkeys->enc.iv, newkeys->enc.iv_len); + free(newkeys->enc.iv); + newkeys->enc.iv = NULL; + } + free(newkeys->enc.name); + explicit_bzero(&newkeys->enc, sizeof(newkeys->enc)); + free(newkeys->comp.name); + explicit_bzero(&newkeys->comp, sizeof(newkeys->comp)); + mac_clear(&newkeys->mac); + if (newkeys->mac.key) { + explicit_bzero(newkeys->mac.key, newkeys->mac.key_len); + free(newkeys->mac.key); + newkeys->mac.key = NULL; + } + free(newkeys->mac.name); + explicit_bzero(&newkeys->mac, sizeof(newkeys->mac)); + freezero(newkeys, sizeof(*newkeys)); +} + +void +kex_free(struct kex *kex) +{ + u_int mode; + + if (kex == NULL) + return; + +#ifdef WITH_OPENSSL + DH_free(kex->dh); +#ifdef OPENSSL_HAS_ECC + EC_KEY_free(kex->ec_client_key); +#endif /* OPENSSL_HAS_ECC */ +#endif /* WITH_OPENSSL */ + for (mode = 0; mode < MODE_MAX; mode++) { + kex_free_newkeys(kex->newkeys[mode]); + kex->newkeys[mode] = NULL; + } + sshbuf_free(kex->peer); + sshbuf_free(kex->my); + sshbuf_free(kex->client_version); + sshbuf_free(kex->server_version); + sshbuf_free(kex->client_pub); + free(kex->session_id); + free(kex->failed_choice); + free(kex->hostkey_alg); + free(kex->name); + free(kex); +} + +int +kex_ready(struct ssh *ssh, char *proposal[PROPOSAL_MAX]) +{ + int r; + + if ((r = kex_prop2buf(ssh->kex->my, proposal)) != 0) + return r; + ssh->kex->flags = KEX_INITIAL; + kex_reset_dispatch(ssh); + ssh_dispatch_set(ssh, SSH2_MSG_KEXINIT, &kex_input_kexinit); + return 0; +} + +int +kex_setup(struct ssh *ssh, char *proposal[PROPOSAL_MAX]) +{ + int r; + + if ((r = kex_ready(ssh, proposal)) != 0) + return r; + if ((r = kex_send_kexinit(ssh)) != 0) { /* we start */ + kex_free(ssh->kex); + ssh->kex = NULL; + return r; + } + return 0; +} + +/* + * Request key re-exchange, returns 0 on success or a ssherr.h error + * code otherwise. Must not be called if KEX is incomplete or in-progress. + */ +int +kex_start_rekex(struct ssh *ssh) +{ + if (ssh->kex == NULL) { + error("%s: no kex", __func__); + return SSH_ERR_INTERNAL_ERROR; + } + if (ssh->kex->done == 0) { + error("%s: requested twice", __func__); + return SSH_ERR_INTERNAL_ERROR; + } + ssh->kex->done = 0; + return kex_send_kexinit(ssh); +} + +static int +choose_enc(struct sshenc *enc, char *client, char *server) +{ + char *name = match_list(client, server, NULL); + + if (name == NULL) + return SSH_ERR_NO_CIPHER_ALG_MATCH; + if ((enc->cipher = cipher_by_name(name)) == NULL) { + error("%s: unsupported cipher %s", __func__, name); + free(name); + return SSH_ERR_INTERNAL_ERROR; + } + enc->name = name; + enc->enabled = 0; + enc->iv = NULL; + enc->iv_len = cipher_ivlen(enc->cipher); + enc->key = NULL; + enc->key_len = cipher_keylen(enc->cipher); + enc->block_size = cipher_blocksize(enc->cipher); + return 0; +} + +static int +choose_mac(struct ssh *ssh, struct sshmac *mac, char *client, char *server) +{ + char *name = match_list(client, server, NULL); + + if (name == NULL) + return SSH_ERR_NO_MAC_ALG_MATCH; + if (mac_setup(mac, name) < 0) { + error("%s: unsupported MAC %s", __func__, name); + free(name); + return SSH_ERR_INTERNAL_ERROR; + } + mac->name = name; + mac->key = NULL; + mac->enabled = 0; + return 0; +} + +static int +choose_comp(struct sshcomp *comp, char *client, char *server) +{ + char *name = match_list(client, server, NULL); + + if (name == NULL) + return SSH_ERR_NO_COMPRESS_ALG_MATCH; +#ifdef WITH_ZLIB + if (strcmp(name, "zlib@openssh.com") == 0) { + comp->type = COMP_DELAYED; + } else if (strcmp(name, "zlib") == 0) { + comp->type = COMP_ZLIB; + } else +#endif /* WITH_ZLIB */ + if (strcmp(name, "none") == 0) { + comp->type = COMP_NONE; + } else { + error("%s: unsupported compression scheme %s", __func__, name); + free(name); + return SSH_ERR_INTERNAL_ERROR; + } + comp->name = name; + return 0; +} + +static int +choose_kex(struct kex *k, char *client, char *server) +{ + const struct kexalg *kexalg; + + k->name = match_list(client, server, NULL); + + debug("kex: algorithm: %s", k->name ? k->name : "(no match)"); + if (k->name == NULL) + return SSH_ERR_NO_KEX_ALG_MATCH; + if ((kexalg = kex_alg_by_name(k->name)) == NULL) { + error("%s: unsupported KEX method %s", __func__, k->name); + return SSH_ERR_INTERNAL_ERROR; + } + k->kex_type = kexalg->type; + k->hash_alg = kexalg->hash_alg; + k->ec_nid = kexalg->ec_nid; + return 0; +} + +static int +choose_hostkeyalg(struct kex *k, char *client, char *server) +{ + k->hostkey_alg = match_list(client, server, NULL); + + debug("kex: host key algorithm: %s", + k->hostkey_alg ? k->hostkey_alg : "(no match)"); + if (k->hostkey_alg == NULL) + return SSH_ERR_NO_HOSTKEY_ALG_MATCH; + k->hostkey_type = sshkey_type_from_name(k->hostkey_alg); + if (k->hostkey_type == KEY_UNSPEC) { + error("%s: unsupported hostkey algorithm %s", __func__, + k->hostkey_alg); + return SSH_ERR_INTERNAL_ERROR; + } + k->hostkey_nid = sshkey_ecdsa_nid_from_name(k->hostkey_alg); + return 0; +} + +static int +proposals_match(char *my[PROPOSAL_MAX], char *peer[PROPOSAL_MAX]) +{ + static int check[] = { + PROPOSAL_KEX_ALGS, PROPOSAL_SERVER_HOST_KEY_ALGS, -1 + }; + int *idx; + char *p; + + for (idx = &check[0]; *idx != -1; idx++) { + if ((p = strchr(my[*idx], ',')) != NULL) + *p = '\0'; + if ((p = strchr(peer[*idx], ',')) != NULL) + *p = '\0'; + if (strcmp(my[*idx], peer[*idx]) != 0) { + debug2("proposal mismatch: my %s peer %s", + my[*idx], peer[*idx]); + return (0); + } + } + debug2("proposals match"); + return (1); +} + +static int +kex_choose_conf(struct ssh *ssh) +{ + struct kex *kex = ssh->kex; + struct newkeys *newkeys; + char **my = NULL, **peer = NULL; + char **cprop, **sprop; + int nenc, nmac, ncomp; + u_int mode, ctos, need, dh_need, authlen; + int r, first_kex_follows; + + debug2("local %s KEXINIT proposal", kex->server ? "server" : "client"); + if ((r = kex_buf2prop(kex->my, NULL, &my)) != 0) + goto out; + debug2("peer %s KEXINIT proposal", kex->server ? "client" : "server"); + if ((r = kex_buf2prop(kex->peer, &first_kex_follows, &peer)) != 0) + goto out; + + if (kex->server) { + cprop=peer; + sprop=my; + } else { + cprop=my; + sprop=peer; + } + + /* Check whether client supports ext_info_c */ + if (kex->server && (kex->flags & KEX_INITIAL)) { + char *ext; + + ext = match_list("ext-info-c", peer[PROPOSAL_KEX_ALGS], NULL); + kex->ext_info_c = (ext != NULL); + free(ext); + } + + /* Algorithm Negotiation */ + if ((r = choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], + sprop[PROPOSAL_KEX_ALGS])) != 0) { + kex->failed_choice = peer[PROPOSAL_KEX_ALGS]; + peer[PROPOSAL_KEX_ALGS] = NULL; + goto out; + } + if ((r = choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS], + sprop[PROPOSAL_SERVER_HOST_KEY_ALGS])) != 0) { + kex->failed_choice = peer[PROPOSAL_SERVER_HOST_KEY_ALGS]; + peer[PROPOSAL_SERVER_HOST_KEY_ALGS] = NULL; + goto out; + } + for (mode = 0; mode < MODE_MAX; mode++) { + if ((newkeys = calloc(1, sizeof(*newkeys))) == NULL) { + r = SSH_ERR_ALLOC_FAIL; + goto out; + } + kex->newkeys[mode] = newkeys; + ctos = (!kex->server && mode == MODE_OUT) || + (kex->server && mode == MODE_IN); + nenc = ctos ? PROPOSAL_ENC_ALGS_CTOS : PROPOSAL_ENC_ALGS_STOC; + nmac = ctos ? PROPOSAL_MAC_ALGS_CTOS : PROPOSAL_MAC_ALGS_STOC; + ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC; + if ((r = choose_enc(&newkeys->enc, cprop[nenc], + sprop[nenc])) != 0) { + kex->failed_choice = peer[nenc]; + peer[nenc] = NULL; + goto out; + } + authlen = cipher_authlen(newkeys->enc.cipher); + /* ignore mac for authenticated encryption */ + if (authlen == 0 && + (r = choose_mac(ssh, &newkeys->mac, cprop[nmac], + sprop[nmac])) != 0) { + kex->failed_choice = peer[nmac]; + peer[nmac] = NULL; + goto out; + } + if ((r = choose_comp(&newkeys->comp, cprop[ncomp], + sprop[ncomp])) != 0) { + kex->failed_choice = peer[ncomp]; + peer[ncomp] = NULL; + goto out; + } + debug("kex: %s cipher: %s MAC: %s compression: %s", + ctos ? "client->server" : "server->client", + newkeys->enc.name, + authlen == 0 ? newkeys->mac.name : "<implicit>", + newkeys->comp.name); + } + need = dh_need = 0; + for (mode = 0; mode < MODE_MAX; mode++) { + newkeys = kex->newkeys[mode]; + need = MAXIMUM(need, newkeys->enc.key_len); + need = MAXIMUM(need, newkeys->enc.block_size); + need = MAXIMUM(need, newkeys->enc.iv_len); + need = MAXIMUM(need, newkeys->mac.key_len); + dh_need = MAXIMUM(dh_need, cipher_seclen(newkeys->enc.cipher)); + dh_need = MAXIMUM(dh_need, newkeys->enc.block_size); + dh_need = MAXIMUM(dh_need, newkeys->enc.iv_len); + dh_need = MAXIMUM(dh_need, newkeys->mac.key_len); + } + /* XXX need runden? */ + kex->we_need = need; + kex->dh_need = dh_need; + + /* ignore the next message if the proposals do not match */ + if (first_kex_follows && !proposals_match(my, peer)) + ssh->dispatch_skip_packets = 1; + r = 0; + out: + kex_prop_free(my); + kex_prop_free(peer); + return r; +} + +static int +derive_key(struct ssh *ssh, int id, u_int need, u_char *hash, u_int hashlen, + const struct sshbuf *shared_secret, u_char **keyp) +{ + struct kex *kex = ssh->kex; + struct ssh_digest_ctx *hashctx = NULL; + char c = id; + u_int have; + size_t mdsz; + u_char *digest; + int r; + + if ((mdsz = ssh_digest_bytes(kex->hash_alg)) == 0) + return SSH_ERR_INVALID_ARGUMENT; + if ((digest = calloc(1, ROUNDUP(need, mdsz))) == NULL) { + r = SSH_ERR_ALLOC_FAIL; + goto out; + } + + /* K1 = HASH(K || H || "A" || session_id) */ + if ((hashctx = ssh_digest_start(kex->hash_alg)) == NULL || + ssh_digest_update_buffer(hashctx, shared_secret) != 0 || + ssh_digest_update(hashctx, hash, hashlen) != 0 || + ssh_digest_update(hashctx, &c, 1) != 0 || + ssh_digest_update(hashctx, kex->session_id, + kex->session_id_len) != 0 || + ssh_digest_final(hashctx, digest, mdsz) != 0) { + r = SSH_ERR_LIBCRYPTO_ERROR; + error("%s: KEX hash failed", __func__); + goto out; + } + ssh_digest_free(hashctx); + hashctx = NULL; + + /* + * expand key: + * Kn = HASH(K || H || K1 || K2 || ... || Kn-1) + * Key = K1 || K2 || ... || Kn + */ + for (have = mdsz; need > have; have += mdsz) { + if ((hashctx = ssh_digest_start(kex->hash_alg)) == NULL || + ssh_digest_update_buffer(hashctx, shared_secret) != 0 || + ssh_digest_update(hashctx, hash, hashlen) != 0 || + ssh_digest_update(hashctx, digest, have) != 0 || + ssh_digest_final(hashctx, digest + have, mdsz) != 0) { + error("%s: KDF failed", __func__); + r = SSH_ERR_LIBCRYPTO_ERROR; + goto out; + } + ssh_digest_free(hashctx); + hashctx = NULL; + } +#ifdef DEBUG_KEX + fprintf(stderr, "key '%c'== ", c); + dump_digest("key", digest, need); +#endif + *keyp = digest; + digest = NULL; + r = 0; + out: + free(digest); + ssh_digest_free(hashctx); + return r; +} + +#define NKEYS 6 +int +kex_derive_keys(struct ssh *ssh, u_char *hash, u_int hashlen, + const struct sshbuf *shared_secret) +{ + struct kex *kex = ssh->kex; + u_char *keys[NKEYS]; + u_int i, j, mode, ctos; + int r; + + /* save initial hash as session id */ + if (kex->session_id == NULL) { + kex->session_id_len = hashlen; + kex->session_id = malloc(kex->session_id_len); + if (kex->session_id == NULL) + return SSH_ERR_ALLOC_FAIL; + memcpy(kex->session_id, hash, kex->session_id_len); + } + for (i = 0; i < NKEYS; i++) { + if ((r = derive_key(ssh, 'A'+i, kex->we_need, hash, hashlen, + shared_secret, &keys[i])) != 0) { + for (j = 0; j < i; j++) + free(keys[j]); + return r; + } + } + for (mode = 0; mode < MODE_MAX; mode++) { + ctos = (!kex->server && mode == MODE_OUT) || + (kex->server && mode == MODE_IN); + kex->newkeys[mode]->enc.iv = keys[ctos ? 0 : 1]; + kex->newkeys[mode]->enc.key = keys[ctos ? 2 : 3]; + kex->newkeys[mode]->mac.key = keys[ctos ? 4 : 5]; + } + return 0; +} + +int +kex_load_hostkey(struct ssh *ssh, struct sshkey **prvp, struct sshkey **pubp) +{ + struct kex *kex = ssh->kex; + + *pubp = NULL; + *prvp = NULL; + if (kex->load_host_public_key == NULL || + kex->load_host_private_key == NULL) { + error("%s: missing hostkey loader", __func__); + return SSH_ERR_INVALID_ARGUMENT; + } + *pubp = kex->load_host_public_key(kex->hostkey_type, + kex->hostkey_nid, ssh); + *prvp = kex->load_host_private_key(kex->hostkey_type, + kex->hostkey_nid, ssh); + if (*pubp == NULL) + return SSH_ERR_NO_HOSTKEY_LOADED; + return 0; +} + +int +kex_verify_host_key(struct ssh *ssh, struct sshkey *server_host_key) +{ + struct kex *kex = ssh->kex; + + if (kex->verify_host_key == NULL) { + error("%s: missing hostkey verifier", __func__); + return SSH_ERR_INVALID_ARGUMENT; + } + if (server_host_key->type != kex->hostkey_type || + (kex->hostkey_type == KEY_ECDSA && + server_host_key->ecdsa_nid != kex->hostkey_nid)) + return SSH_ERR_KEY_TYPE_MISMATCH; + if (kex->verify_host_key(server_host_key, ssh) == -1) + return SSH_ERR_SIGNATURE_INVALID; + return 0; +} + +#if defined(DEBUG_KEX) || defined(DEBUG_KEXDH) || defined(DEBUG_KEXECDH) +void +dump_digest(const char *msg, const u_char *digest, int len) +{ + fprintf(stderr, "%s\n", msg); + sshbuf_dump_data(digest, len, stderr); +} +#endif + +/* + * Send a plaintext error message to the peer, suffixed by \r\n. + * Only used during banner exchange, and there only for the server. + */ +static void +send_error(struct ssh *ssh, char *msg) +{ + char *crnl = "\r\n"; + + if (!ssh->kex->server) + return; + + if (atomicio(vwrite, ssh_packet_get_connection_out(ssh), + msg, strlen(msg)) != strlen(msg) || + atomicio(vwrite, ssh_packet_get_connection_out(ssh), + crnl, strlen(crnl)) != strlen(crnl)) + error("%s: write: %.100s", __func__, strerror(errno)); +} + +/* + * Sends our identification string and waits for the peer's. Will block for + * up to timeout_ms (or indefinitely if timeout_ms <= 0). + * Returns on 0 success or a ssherr.h code on failure. + */ +int +kex_exchange_identification(struct ssh *ssh, int timeout_ms, + const char *version_addendum) +{ + int remote_major, remote_minor, mismatch, oerrno = 0; + size_t len, i, n; + int r, expect_nl; + u_char c; + struct sshbuf *our_version = ssh->kex->server ? + ssh->kex->server_version : ssh->kex->client_version; + struct sshbuf *peer_version = ssh->kex->server ? + ssh->kex->client_version : ssh->kex->server_version; + char *our_version_string = NULL, *peer_version_string = NULL; + char *cp, *remote_version = NULL; + + /* Prepare and send our banner */ + sshbuf_reset(our_version); + if (version_addendum != NULL && *version_addendum == '\0') + version_addendum = NULL; + if ((r = sshbuf_putf(our_version, "SSH-%d.%d-%.100s%s%s\r\n", + PROTOCOL_MAJOR_2, PROTOCOL_MINOR_2, SSH_VERSION, + version_addendum == NULL ? "" : " ", + version_addendum == NULL ? "" : version_addendum)) != 0) { + oerrno = errno; + error("%s: sshbuf_putf: %s", __func__, ssh_err(r)); + goto out; + } + + if (atomicio(vwrite, ssh_packet_get_connection_out(ssh), + sshbuf_mutable_ptr(our_version), + sshbuf_len(our_version)) != sshbuf_len(our_version)) { + oerrno = errno; + debug("%s: write: %.100s", __func__, strerror(errno)); + r = SSH_ERR_SYSTEM_ERROR; + goto out; + } + if ((r = sshbuf_consume_end(our_version, 2)) != 0) { /* trim \r\n */ + oerrno = errno; + error("%s: sshbuf_consume_end: %s", __func__, ssh_err(r)); + goto out; + } + our_version_string = sshbuf_dup_string(our_version); + if (our_version_string == NULL) { + error("%s: sshbuf_dup_string failed", __func__); + r = SSH_ERR_ALLOC_FAIL; + goto out; + } + debug("Local version string %.100s", our_version_string); + + /* Read other side's version identification. */ + for (n = 0; ; n++) { + if (n >= SSH_MAX_PRE_BANNER_LINES) { + send_error(ssh, "No SSH identification string " + "received."); + error("%s: No SSH version received in first %u lines " + "from server", __func__, SSH_MAX_PRE_BANNER_LINES); + r = SSH_ERR_INVALID_FORMAT; + goto out; + } + sshbuf_reset(peer_version); + expect_nl = 0; + for (i = 0; ; i++) { + if (timeout_ms > 0) { + r = waitrfd(ssh_packet_get_connection_in(ssh), + &timeout_ms); + if (r == -1 && errno == ETIMEDOUT) { + send_error(ssh, "Timed out waiting " + "for SSH identification string."); + error("Connection timed out during " + "banner exchange"); + r = SSH_ERR_CONN_TIMEOUT; + goto out; + } else if (r == -1) { + oerrno = errno; + error("%s: %s", + __func__, strerror(errno)); + r = SSH_ERR_SYSTEM_ERROR; + goto out; + } + } + + len = atomicio(read, ssh_packet_get_connection_in(ssh), + &c, 1); + if (len != 1 && errno == EPIPE) { + error("%s: Connection closed by remote host", + __func__); + r = SSH_ERR_CONN_CLOSED; + goto out; + } else if (len != 1) { + oerrno = errno; + error("%s: read: %.100s", + __func__, strerror(errno)); + r = SSH_ERR_SYSTEM_ERROR; + goto out; + } + if (c == '\r') { + expect_nl = 1; + continue; + } + if (c == '\n') + break; + if (c == '\0' || expect_nl) { + error("%s: banner line contains invalid " + "characters", __func__); + goto invalid; + } + if ((r = sshbuf_put_u8(peer_version, c)) != 0) { + oerrno = errno; + error("%s: sshbuf_put: %s", + __func__, ssh_err(r)); + goto out; + } + if (sshbuf_len(peer_version) > SSH_MAX_BANNER_LEN) { + error("%s: banner line too long", __func__); + goto invalid; + } + } + /* Is this an actual protocol banner? */ + if (sshbuf_len(peer_version) > 4 && + memcmp(sshbuf_ptr(peer_version), "SSH-", 4) == 0) + break; + /* If not, then just log the line and continue */ + if ((cp = sshbuf_dup_string(peer_version)) == NULL) { + error("%s: sshbuf_dup_string failed", __func__); + r = SSH_ERR_ALLOC_FAIL; + goto out; + } + /* Do not accept lines before the SSH ident from a client */ + if (ssh->kex->server) { + error("%s: client sent invalid protocol identifier " + "\"%.256s\"", __func__, cp); + free(cp); + goto invalid; + } + debug("%s: banner line %zu: %s", __func__, n, cp); + free(cp); + } + peer_version_string = sshbuf_dup_string(peer_version); + if (peer_version_string == NULL) + error("%s: sshbuf_dup_string failed", __func__); + /* XXX must be same size for sscanf */ + if ((remote_version = calloc(1, sshbuf_len(peer_version))) == NULL) { + error("%s: calloc failed", __func__); + r = SSH_ERR_ALLOC_FAIL; + goto out; + } + + /* + * Check that the versions match. In future this might accept + * several versions and set appropriate flags to handle them. + */ + if (sscanf(peer_version_string, "SSH-%d.%d-%[^\n]\n", + &remote_major, &remote_minor, remote_version) != 3) { + error("Bad remote protocol version identification: '%.100s'", + peer_version_string); + invalid: + send_error(ssh, "Invalid SSH identification string."); + r = SSH_ERR_INVALID_FORMAT; + goto out; + } + debug("Remote protocol version %d.%d, remote software version %.100s", + remote_major, remote_minor, remote_version); + ssh->compat = compat_datafellows(remote_version); + + mismatch = 0; + switch (remote_major) { + case 2: + break; + case 1: + if (remote_minor != 99) + mismatch = 1; + break; + default: + mismatch = 1; + break; + } + if (mismatch) { + error("Protocol major versions differ: %d vs. %d", + PROTOCOL_MAJOR_2, remote_major); + send_error(ssh, "Protocol major versions differ."); + r = SSH_ERR_NO_PROTOCOL_VERSION; + goto out; + } + + if (ssh->kex->server && (ssh->compat & SSH_BUG_PROBE) != 0) { + logit("probed from %s port %d with %s. Don't panic.", + ssh_remote_ipaddr(ssh), ssh_remote_port(ssh), + peer_version_string); + r = SSH_ERR_CONN_CLOSED; /* XXX */ + goto out; + } + if (ssh->kex->server && (ssh->compat & SSH_BUG_SCANNER) != 0) { + logit("scanned from %s port %d with %s. Don't panic.", + ssh_remote_ipaddr(ssh), ssh_remote_port(ssh), + peer_version_string); + r = SSH_ERR_CONN_CLOSED; /* XXX */ + goto out; + } + if ((ssh->compat & SSH_BUG_RSASIGMD5) != 0) { + logit("Remote version \"%.100s\" uses unsafe RSA signature " + "scheme; disabling use of RSA keys", remote_version); + } + /* success */ + r = 0; + out: + free(our_version_string); + free(peer_version_string); + free(remote_version); + if (r == SSH_ERR_SYSTEM_ERROR) + errno = oerrno; + return r; +} + |